Gabrielle Grady, who was trapped inside the car for two hours and died in hospital three days later, and her brother, Ryan, who, was pulled out by police. Photograph: West Mercia Police/PA

A father is facing a life sentence after being convicted of murdering his five-year-old daughter by deliberately driving his car into a freezing river with her inside.

Christopher Grady, 42, was also found guilty of attempting to murder his son, then six, who was also in the car.

Birmingham crown court heard that Grady drove to the house of his estranged partner, Kim Smith, in Evesham, Worcestershire, in February last year, telling her: "You've got 10 seconds to say goodbye to your kids, and then they are dead."

With his daughter, Gabrielle, and son, Ryan, inside the Vauxhall Vectra, Grady circled a field before driving at speed into the river Avon. Two police officers pulled Ryan from the water but Gabrielle was trapped inside the vehicle for two hours. She died in hospital three days later.

The jury took five hours to deliver an 11-1 majority verdict that he intended to kill his children. The judge, Mr Justice Lindblom, adjourned sentencing until next week but told Grady that he faced a mandatory life sentence.

The court heard that Grady, who had regular access to his children following the breakdown of his seven-year relationship with Smith, faced personal and financial difficulties and had been evicted from his flat.

West Mercia police were contacted six times about Grady's behaviour before the murder. However, an investigation overseen by the Independent Police Complaints Commission ruled that officers could not have prevented the tragedy.

Smith, reading a brief statement on the steps of the court, said: "Although Christopher Grady is facing a deserved jail term, this does not take away the fact that myself and my family were robbed of our Gabby just over one year ago and that will stay. We are still living with the loss and devastation.

"What must also not be forgotten is what my son Ryan also went through on that day – not only the trauma of the events but that he also lost his sister, who was also his best friend."

Asked about the morning of the murder, Smith said: "Horrifying, the worst experience ever, absolutely shook to the core. He said, 'Be outside, you have 10 seconds to say ta-ra to the children, the kids'."

Grady's mother, Valerie Hubbarb, said: "Unfortunately there are no winners in this case. We are all losers, as our darling Gabby is no longer with us."

The officer in charge of the case, Superintendent Steve Cullen, praised the two officers who rescued Ryan, adding: "I would like to mention the force's admiration for Gabby and Ryan's mum, Kim, and the rest of their family for the dignity and strength they have shown."